Regulation of M2-type pyruvate kinase mediated by the high-affinity IgE receptors is required for mast cell degranulation

Background and purpose: M-2-type pyruvate kinase (M2PK) was found to interact directly with the 'ITAM' region of the g chain of the high-affinity IgE receptor (Fc epsilon RI). Our hypothesis was that mast cell degranulation might require the Fc epsilon RI-mediated inhibition of M2PK activity. Experimental approach: In rat basophilic leukaemia (RBL-2H3) cells, the effects of directly inhibiting M2PK or preventing the Fc epsilon RI-mediated inhibition of M2PK (disinhibition) on degranulation was measured by hexosaminidase release. Effects of blocking the Fc epsilon RI-mediated inhibition of M2PK was also assessed in vivo in a mouse model of allergen-induced airway hyper-responsiveness. Key results: Activation of Fc epsilon RI in RBL-2H3 cells caused the rapid phosphorylation of tyrosine residues in M2PK, associated with a decrease in M2PK enzymatic activity. There was an inverse correlation between M2PK activity and mast cell degranulation. Fc epsilon RI-mediated inhibition of M2PK involved Src kinase, phosphatidylinositol 3-kinase, PKC and calcium. Direct inhibition of M2PK potentiated Fc epsilon RI-mediated degranulation and prevention of the Fc epsilon RI-mediated inhibition of M2PK attenuated mast cell degranulation. Transfection of RBL-2H3 cells with M1PK which prevents Fc epsilon RI-induced inhibition of M2PK, markedly reduced their degranulation and exogenous M1PK (i.p.) inhibited ovalbumin-induced airway hyper-responsiveness in vivo. Conclusions and implications: We have identified a new control point and a novel biochemical pathway in the process of mast cell degranulation. Our study suggests that the Fc epsilon RI-mediated inhibition of M2PK is a crucial step in responses to allergens. Moreover, the manipulation of glycolytic processes and intermediates could provide novel strategies for the treatment of allergic diseases.